Federer and Zverev after the latter's victory. Zverev immediately signalled for the point to be stopped and the umpire ordered the point to be replayed.

"Overall it was a phenomenal season that I have to be definitely very proud of", Djokovic said. "The ball boy dropped the ball so it's in the rules that we have to replay the point".

"I'm a little bit upset about the whole situation because this is not how I wanted it to end".

He began it by taking the Jubilee line to Westminster along with all the other competitors in the ATP World Tour Finals to meet Speaker of the House of Commons John Bercow. However, again, I'd have been more tempted with slightly bigger, although it's worth noting that when similarly priced, he has shown a tendency to be more competitive in the first set than for subsequent ones.

Victory against Djokovic at the O2 Arena would surely go down as his biggest triumph.

"When you get out of this feeling of a little bit disappointment that you lost, I mean, all the positive things that I have to reflect on and also take from this season, especially the last six months".

Anderson beat Isner 26-24 in the final set after a six hour, 36 minute battle - the second longest match in Wimbledon history which prompted organisers to limit final sets to a maximum of 24 games before a tie-break kicks in at 12-all to settle matters from 2019 onwards.

Federer willed himself to a break for 2-1 in the second set, but Zverev quickly composed himself to hit straight back in the following game.

"From that standpoint, it's OK, no problem, that happens", said the Swiss.

Despite having reached only one Grand Slam quarterfinal this year, Zverev is the only active player outside the Big Four of Djokovic, Federer, Rafael Nadal and Andy Murray to have won three Masters titles. But victory at the tour's flagship event would exceed those achievements.

Kevin Anderson felt the relentless pressure from Novak Djokovic during the semi-final of the ATP Finals in London on Saturday night. "And he's returning well, which definitely makes life hard, but that's why he's one of the best players of all time". "I hope I'll be able to do that tomorrow".

"I played very well in the group stage against Sascha (Zverev)", Djokovic said. If he's serving well, I think even Novak has troubles.

Djokovic won 20 out of 27 points on Anderson's second serve as he broke the South African twice in each set.

"I will do everything I can to get better, to compete with them always".

Anderson nicked one game back but it was a hopeless task and Djokovic put him out of his misery with a netcord on matchpoint to claim a 35th win in his last 37 matches - a run including the Wimbledon and U.S. Open titles to swell his collection of Grand Slam titles to 14.

Djokovic had a hard start to the season as he was struggling to recover from an elbow injury that had seen him skip the second half of last season.